1. Field of the Invention
The invention relates to a method for producing a magnetic recording medium by means of magnetron sputtering and more particularly relates to a method for producing a Mn-Al .tau.-phase thin film.
2. Description of the Prior Art
Recently, the amount of information storage is increased rapidly due to the rapid development of the computer industry. In order to get high recording density, the magnetic recording media have been improved from the conventional .gamma.-Fe.sub.2 O.sub.3 particles system to the thin film media.
A high recording density thin film medium needs high coercity force, high saturation magnetization, high stability and high wear resistance.
In the present thin film recording media, the CoCrM (M=Ni, Pt, Ta) thin films are the most widely used materials due to its high coercivity Hc (1500-1800 Oe) and high saturation magnetization Ms (600-1200 emu/cc). However, these metal thin films still have some drawbacks such as the high cost of the raw materials, low coercivity, the corrosion problem, the low hardness and the complicated fabrication process.
In order to overcome these problems many investigatiors studies the oxide films. Although the oxide films have better characteristics about the deficiencies of the CoCrM films described above, the magnetic properties of the oxide films are poorer than the metal films. For example, the saturation magnetization and coercivity of the .gamma.-Fe.sub.2 O.sub.3 film are about 300 emu/cc and 300 Oe, respectively. The coercivity of .gamma.-Fe.sub.2 O.sub.3 may be increased by doping Co element, but the thermal stability is decreased due to that the considerable variation of the crystal anisotropy constant of the Co-.gamma.-Fe.sub.2 O.sub.3 with temperature.
Since the present magnetic recording media have to improve further to cope with the ever-increasing demand of recording density, many investigators try to find some novel recording materials; among them, Mn-Al thin films are examplary. The Mn-Al .tau.-phase is a promising material for magnetic recording media because it has a high magnetic anisotry constant, high hardness and high stability. In addition, it comprises of low-cost materials instead of scarce materials such as Co, Ni, Ta and Pt. And the magnetic recording media for the MR magnetic head which will be used in future needs a high Hc value above 2500 Oe. The Mn-Al thin film produced in this invention has high Hc value up to about 3000 Oe. Therefore, this Mn-Al thin film may become the high density recording media in the future.
According to the literature (A. Morisako and M. Matsumoto, "Synthsis of the ferromagnetic .tau.-phase of Mn-Al film by sputtering", J.Appl. Phys. vol. 61, no. 8, p 4281, 1987), ferromagnetic .tau.-phase of Mn-Al thin films were synthesized at Mn constant of about 60 at. % and substrate temperature of about 150.degree. C. However, these films exhibited low saturation magnetization which is 120 emu/cc. It is only one-fourth of the bulk material. Obviously, their Mn-Al films are not pure .tau.-phase. Further investigations (M. Matsumoto, A. Morisaka, and J. Oshima, "Properties of ferromagnetic Mn-Al thin films with additives", J. Appl. Phys., vol. 69, no. 8, p. 5172, 1991) were studied by doping the elements such as Cu, Ni, Fe, Co, Ag, Zn; they found a maximum saturation magnetization of about 300 emu/cc for a Mn.sub.38 -Al.sub.40 -Cu.sub.22 thin film, however its coercivity decrease to about 220 Oe. These films were composed of both the Mn-Al .tau.-phase and Mn-Al-Cu .kappa.-phase. The two methods described above did not produced the pure .tau.-phase successful. So, the magnetic properties of their films are not good. The single ferromagnetic Mn-Al .tau.-phase has not been fabricated before.